I can confirm that using My Little Warband (1.7) with Party AI Overhaul Commands Rebuild (1.7) does allow your parties to recruit your custom troops exclusively. Following these steps will cause any troops your parties recruit to automatically transform into your custom troops, regardless of what faction they recruit from*:

1.) Using My Little Warband (default settings), create your custom desired troops for both recruit and elite trees.
2.) Using Party AI Overhaul (default settings), after forming your desired party, talk to the party leader.
3.) Select > "Let's review your party's composition plan."
4.) Select > "Let's decide what troops you should recruit."
5.) Under "Available Troop Trees" hit the transfer all button until all the troops on the right are transferred to the left.
6.) Select > "Let's have a closer look."
7.) Do not change anything here. Select > Done.
8.) Finally, you will be asked if you wish to recruit from prisoners. Select > "No." (Choosing "Yes" will allow them to recruit looters. However, after testing, looter troops recruited by parties stay looters and do not transform into your custom troops. So Select > "Yes" if you don't mind having looters mixed in with your custom troops.)

For some reason, I personally have found that doing this any other way causes the party never to recruit anyone.

*Please note that this will allow only the player's parties the ability to recruit your custom troops. If you would like other AI lords to be able to recruit your custom troops also, then you will need to change the xml settings in My Little Warband.